Self-Healing Cement for Long-Term Safe Exploitation of Gas Wells: A New Technology Case Study
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Cited by 4 publications
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Energy Transition by Employing a Self-Healing, Reduced Carbon Dioxide Footprint Sealant in a Strategic Underground Gas Storage Project
The Tuz Gölü underground gas storage (UGS) project is a strategic venture in Turkey's energy program. This gas storage facility will be the largest in Europe, having multibillion m3 capacity, by taking advantage of the optimal gas storage conditions offered by subterranean salt caverns. Upon reaching the reservoir, one of the important goals is to obtain hydraulic isolation between the surface and the casing. Inadequate downhole isolation may well result in interzonal communication, gas migration, casing corrosion, and sustained casing pressure. Furthermore, gas flow to surface formations and/or to the atmosphere, could impact the environment and health along with an underlying economic impact. Wellbore isolation was introduced in the form of fully salt-saturated gas control and self-healing cement systems. When drilling into salt caverns, the foremost challenge is to minimize the dissolution of the in-situ salt formation by means of contact with water-based cementing fluids, which can lead to the creation of new flow paths. This occurrence must be prevented at all costs; otherwise, stored gas might leak through these microchannels. Unlike typical salt formations, this candidate field also contains carbon dioxide (CO2). Most wells in the field had a prognosis toward low CO2 content, so cement exposure to CO2 was not deemed an elevated risk; however, if the CO2 exposure risk increased, it would potentially generate an additional challenge both in terms of gas migration control and long-term cement integrity. Currently, more than 100 cementing operations have been performed in the candidate field. After pumping 3,500 metric ton of cement and blending 750 metric ton of the tailored self-healing cement, more than 300 laboratory tests were performed. More than 15,000 staff-hours of testing supported construction of 32 UGS wells, fully cemented with zero health, safety, and environment (HSE) or service quality incidents and, importantly, with outstanding bond log results. Completion strings in 15 wells have already been run where wells are prepared to store gas; the ongoing project is now expanded to 50 UGS wells. Furthermore, an intrinsic benefit of the self-healing cement system is reduced CO2 footprint vs. conventional class G cement, which can be nominally 40% less CO2 per unit volume. With involvement of local laboratories and technical experts in the region, salt-saturated gas-control and self-healing cement slurry systems have been developed and successfully deployed. Information regarding these system's liquid and set properties will be presented, along with techniques used to enhance certain cement properties. The field cases that will be presented describe how challenges were overcome in successfully sealing UGS wells in a highly saline environment, and how the self-healing technology applied in these wells is being extended to include salt-saturated systems and CO2-resistant versions elsewhere.
Energy Transition by Employing a Self-Healing, Reduced Carbon Dioxide Footprint Sealant in a Strategic Underground Gas Storage Project
The Tuz Gölü underground gas storage (UGS) project is a strategic venture in Turkey's energy program. This gas storage facility will be the largest in Europe, having multibillion m3 capacity, by taking advantage of the optimal gas storage conditions offered by subterranean salt caverns. Upon reaching the reservoir, one of the important goals is to obtain hydraulic isolation between the surface and the casing. Inadequate downhole isolation may well result in interzonal communication, gas migration, casing corrosion, and sustained casing pressure. Furthermore, gas flow to surface formations and/or to the atmosphere, could impact the environment and health along with an underlying economic impact. Wellbore isolation was introduced in the form of fully salt-saturated gas control and self-healing cement systems. When drilling into salt caverns, the foremost challenge is to minimize the dissolution of the in-situ salt formation by means of contact with water-based cementing fluids, which can lead to the creation of new flow paths. This occurrence must be prevented at all costs; otherwise, stored gas might leak through these microchannels. Unlike typical salt formations, this candidate field also contains carbon dioxide (CO2). Most wells in the field had a prognosis toward low CO2 content, so cement exposure to CO2 was not deemed an elevated risk; however, if the CO2 exposure risk increased, it would potentially generate an additional challenge both in terms of gas migration control and long-term cement integrity. Currently, more than 100 cementing operations have been performed in the candidate field. After pumping 3,500 metric ton of cement and blending 750 metric ton of the tailored self-healing cement, more than 300 laboratory tests were performed. More than 15,000 staff-hours of testing supported construction of 32 UGS wells, fully cemented with zero health, safety, and environment (HSE) or service quality incidents and, importantly, with outstanding bond log results. Completion strings in 15 wells have already been run where wells are prepared to store gas; the ongoing project is now expanded to 50 UGS wells. Furthermore, an intrinsic benefit of the self-healing cement system is reduced CO2 footprint vs. conventional class G cement, which can be nominally 40% less CO2 per unit volume. With involvement of local laboratories and technical experts in the region, salt-saturated gas-control and self-healing cement slurry systems have been developed and successfully deployed. Information regarding these system's liquid and set properties will be presented, along with techniques used to enhance certain cement properties. The field cases that will be presented describe how challenges were overcome in successfully sealing UGS wells in a highly saline environment, and how the self-healing technology applied in these wells is being extended to include salt-saturated systems and CO2-resistant versions elsewhere.
An operator had a need to cement a 13⅜-in. casing to act as a secondary barrier against a reservoir with the top of cement 100 m above a sand formation. In a subsequent section, the operator required installing and cementing a 9⅝-in. liner as the primary barrier element prior to drilling into the reservoir and placing the top of cement up to the 13 ⅜-in. casing shoe. The operation required placing a minimum 30 m of isolating cement in the cemented interval, where verification of the barrier was to be obtained by using logging tools. To comprehend the operating environment the cement would experience, it was necessary to determine an optimal cement system for the anticipated pressure and temperature cycles in the well. The service company performed a cement integrity evaluation using specialized cement sheath stress analysis software. The simulation software determined which cement system was best suited for exposure to the anticipated pressure and temperature cycles during injection and production. Based on the simulation results, the operator decided to use an environmentally compliant flexible (ECF) cement system. This novel system also significantly reduced the CO2 emissions (CO2e) footprint vs. conventional cement. The operator drilled the 17½-in. open hole to 1888 m measured depth (MD) without any issues using a proprietary flat rheology drilling fluid system. A total of 18.9 m3 of 1.60 specific gravity (SG) ECF cement slurry was pumped. During displacement, no losses were observed as the spacer entered the annulus, and consistent lift pressure was observed as the cement entered the annulus. The job signature pressure match conducted using proprietary zonal isolation software indicated that the openhole size was near gauge hole. The 12¼-in. open hole was drilled, and the 9⅝-in. liner was successfully run to total depth without incident. A total of 16.1 m3 of 1.60 SG ECF cement slurry was pumped. No losses were observed during the cementing operation, and consistent lift pressure was recorded during displacement. The liner was logged using ultrasonic imaging tools, with the top-of-cement bond identified at the 13⅜-in. casing shoe with a total 248 m of isolating cement. The operation achieved the required isolation to install the cemented liner as the primary barrier element prior to drilling into the reservoir, in addition to the exceptional logging results. The ECF cement system provided outstanding bond quality from 1882 to 2130 m. Remarkably, as an energy transition technology when compared with a conventional foamed cement system, the ECF cement system reduced CO2 emissions by 44% and simplified the operation by eliminating the use of foamed cement. Furthermore, the ECF cement is environmentally rated as PLONOR (poses little or no risk) and eliminates the use of polymeric materials to impart flexibility.
Underground gas storage (UGS) wells have emerged as a strategic solution in China. Success of UGS projects largely depends upon maintaining long term well integrity. Cement slurries that are placed across a wellbore should exhibit superior cement bonding as evidenced through a cement bond log (CBL) and long-term integrity to sustain the cyclic stress change by the injection and production process. Such slurries should have improved mechanical properties and the job execution should follow all cementing best practices. The well architecture included a 9 5/8-in. surface casing and a 7-in. production liner. The 7-in. Liner was run inside an 8.5-in. open hole and extended to surface using a tie-back liner. This well architecture should have a superior quality of cement across the entire liner. Multiple Finite Element Analysis (FEA) runs were performed to determine an optimum Young's modulus and Poisson Ratio for the cement slurry. These rigorous tests can take weeks to complete. As the well was shallow, to cover a wide range of well profiles, three different slurries were tested prior to the job. The initial mud weight planned for the well was in the range of 1.25 g/cm3 to 1.4 g/cm3. Due to gas influx, the mud density in the section was increased to 1.90 g/cm3. However, losses were also encountered at this mud density. Hydraulic modelling was revised, and slurry rheology and pumping rates were optimized to ensure equivalent circulation density (ECD) control within the pore pressure and fracture gradient window. Displacement rates were optimized to facilitate good displacement efficiency for hole cleaning. The slurry design was tailored with special additives to provide a synergetic effect of improving mechanical properties and minimizing seepage losses. Multiple computational fluid dynamics (CFD) runs were performed to evaluate the cementing job quality and based on the simulations it was decided to increase the cement volume to minimize any impact of contamination. The cementing job was performed with no operational issues and cement returns were observed above the top of the liner. Two different cement evaluation logs - CBL and ultra-sonic log, were conducted and showed good cement quality in the open hole section, meeting the well objectives. With this successful implementation, the tailored engineered cementing solution was highly recognized. The design and execution methodology were highlighted as the guideline for further successful cementing operations in UGS projects. This study shows a fully comprehensive and scientific way to improve cementing quality for long-term well integrity for UGS projects.
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